The L-type calcium channel blocker nimodipine mitigates "learned helplessness" in rats

We assessed the effect of nimodipine, an L-type calcium channel blocker, on the escape deficit induced by prior exposure to inescapable shock in rats in four experiments. In Experiment 1, we injected rats at each of three time points (i.e., before shock exposure, after shock exposure, and before shuttle escape testing) with one of four doses of nimodipine (0, 0.5, 2.5, 5.0 mg/kg). The 5.0-mg/kg dose was most effective, acting to reduce shuttle escape latencies of inescapably shocked rats to a level comparable with nonshocked controls. No benefit occurred in Experiment 2, however, when nimodipine was administered at only one of the three time points used in the first experiment. Moreover, escape performance did not improve when rats received injections of nimodipine on the 2 days prior the experiment, and then one additional injection at one of the three time points identified above in Experiment 3. Finally, administration of nimodipine at two of the three time points did improve escape responding, but only when injected immediately prior both to shock exposure and the shuttle escape test.